The present invention relates to an acoustic ear muff of the kind which includes a pad of rigid material which has provided therein an opening for accommodating one ear of the wearer and an elastic sealing annulus which is located around the edge of the opening and intended for abutment with head of said wearer, and which ear muff further includes a sprung pressing means attached to the shell of a protective helmet, to a head strap or to like head gear.
Persons who stay in noisy environments for any length of time need some form of protection against the noise. Such protective devices often have the form of ear muffs carried on a protective helmet, such as those worn by forestry workers and mine workers, and by people working on building or construction sites, ship building yards, and like locations.
Two requirements can be placed on an effective acoustic ear muff, i.e. the ability of the ear muff to dampen noise and its capability of being worn comfortably. These two requirements, however, are mutually counterproductive in the main and cannot both be fulfilled satisfactorily in practice at one and the same time. For example, in order to afford a good sound damping effect, if must be possible to hold the ear muff tightly against the head, so as to eliminate the presence of noise-leaking pasageways between the sealing annulus of the ear muff and the head. When worn tightly on the head, however, the ear muff will cause discomfort and even pain, and may also give rise to a rash or the like in the contact area. From the aspect of comfort, the force with which the ear muff is pressed against the head shoulder be as small as possible, which results in poor acoustic damping, however.
Tests have shown that if, whilst in a noisy environment, it is necessary to remove the ear muff for as long as 10% of the total period which the person concerned remains in the area, the risk of damage to the hearing is no smaller than if no ear muff were worn at all.
Hearing damage is likely even when the ear muff is removed for a period as short as 3% of the total period, and a period as short as 1% of the total period results in a marked impairment in the overall protection afforded by the ear muff. The conclusion to be drawn from this is that it is not worthwhile to strive for the best possible acoustic damping effect if the price to be paid is that of comfort, so that the wearer is forced to remove the ear muffs during his presence in a noisy environment.
Prior known acoustic ear muffs available commercially have normally been so constructed as to provide good acoustic damping with head sizes above a given minimum size and a good degree of comfort with sizes beneath a given maximum size. In the case of large heads, the ear muffs lie too tightly against the head and are therefore less comfortable, whereas in the case of small heads the force with which the ear muffs bear against the head is much too small to achieve good acoustic damping. The difference in the force with which the ear muffs are pressed against the head, hereinafter referred to as the pressing force, can vary by 300% between small and large heads. Ear muffs are to be found which can be adjusted to different head sizes. These adjustable ear muffs, however, have not been found satisfactory.
SE-B-7904611-6 teaches an ear-muff attachment device which, in an attempt to achieve a substantially constant pressing force, uses a cup spring and an arm which co-acts with the convex side of the spring. This embodiment also has certain drawbacks.